1. Field of the Invention
The present invention relates to a tilt steering apparatus for a vehicle, mounted with a tilt lock mechanism capable of adjusting the height of the steering wheel of the vehicle according to the physical figure (physique) or driving posture of a driver.
2. Description of the Related Art
A tilt steering apparatus mounted with a tilt lock mechanism is disclosed in a number of publications, for example, U.S. Pat. Nos. 6,481,310, 6,282,977, 5,452,624, 5,143,402, 5,078,022, 4,903,540, and 4,892,330; Japanese Patent Publications Nos. 2000-272524, 1999-268654, 1999-208483, 1999-198819, 1999-129914, 1998-138934, 1996-230687; and Japanese Utility Model Publications Nos. 1994-1110, 1991-112468, 1989-51567, 1988-52666, 1988-12470, 1985-144569, and 1982-142677.
The tilt lock mechanism introduced in the above publications is composed of a fixed gear, a movable gear, a wedge member (or lock slider) and a reaction member, which are sequentially disposed perpendicular to an operating plane of the movable gear. In particular, the tilt lock mechanism mounted on the steering apparatus discussed in U.S. Pat. No. 628,977, as shown in FIGS. 1 and 2, is composed of a fixed gear 31, a movable gear 32 upon the fixed gear 31, a wedge member 33 disposed at the lower portion of the movable gear 32 in such a manner to be able to slide, and a reaction member 35 for supporting a bottom surface of the wedge member 33.
With the help of such tilt lock mechanism, the movable gear 32 is locked or released as follows. Referring to FIG. 1 first, if a tilt lever 34b is rotated clockwise, a protruded portion 32b of the wedge member 33 correspondingly slides to the right side, and the movable gear 32 is released from the tooth coupling to the fixed gear 31. When the lock is released, an upper column member 15 is tilted with respect to a lower column member 15 so as to set the steering wheel at an appropriate height. On the other hand, if the tilt lever 34b is freed, the tilt lever 34b is rotated counter-clockwise by a spring 30, and the wedge member 33 slides to the left side, sliding in-between the movable gear 32 and the reaction member 35, and pushes the movable gear 32 up to be toothed on the fixed gear 31. In this way, the height of the steering wheel can be adjusted as desired.
However, according to the related art tilt steering apparatus, because the protruded portion on the lower end of the wedge member 33 is too little, a heavy load is often placed on the wedge member 33 for breaking the movable away from the fixed gear. This is actually the major cause of changes in operational load or overload on the tilt lever for lock release. As a result, the operability of the tilt lever is substantially lowered.
As an attempt to improve the operability of the tilt lever, U.S. Pat. No. 5,078,022 disclosed a modified tilt lock mechanism as illustrated in FIGS. 3 and 4. In case of the tilt steering apparatus in this disclosure, when a follower gear 34′ of a follower teeth 35′ engageable with the driving teeth 37′ formed on the end of the tilt lever 26′ rotates a shaft 28′, a movable gear 12′ is pushed up by the rotation of an eccentric cam portion 31′ formed on the shaft 28′, and engaged with a fixed gear 9′.
However, because this eccentric cam portion 31′ releases the lock by pressing the movable gear 12′, the movable gear 12′ is easily abraded by the rotation of the eccentric cam portion 31′. As a result thereof, the movable gear 12′ is not perfectly locked or toothed on the fixed gear 9′.
Moreover, the movable gear 12′ is locked or released from the fixed gear 9′ along the circular arc of a flat surface of the eccentric cam portion 31′ or to the opposite direction thereof. Basically, this irregular interval contributes to the operational load or overload on the tilt lever, only resulting in deterioration of tilt lever's operability and generation of noise.